1. Field of the Invention
The present invention relates to a probe unit for examining the electrical characteristics of a target object, particularly, to a fixing mechanism of a probe card for fixing a probe card arranged within a body of a probe unit, i.e., a fixing mechanism of a probe card, which permits suppressing the thermal deformation of the probe card during examination under high-temperature.
2. Description of the Related Art
In the manufacturing process of a semiconductor device, used is an examining apparatus, e.g., a probe unit as shown in FIG. 1, which is called a prober, for examining the electrical characteristics of a plurality of devices formed on a wafer. The probe unit shown in FIG. 1 comprises a loader chamber 1 for receiving wafers W therein and equipped with a mechanism for transferring the wafers W, and a probe chamber 2 for examining the electrical characteristics of the wafer W transferred from the loader chamber 1. Each of the wafer W is pre-aligned in the transfer process of the wafer W in the loader chamber 1, and the electrical characteristic of the wafer W is examined in the probe chamber 2.
In the prober chamber 2, the pre-aligned wafer W is disposed on a main chuck 3 provided with a heating source for heating the wafer W and maintaining the wafer at a predetermined temperature. The main chuck 3 is arranged on an XY table 4 that permits the wafer W to be moved in the X-direction and the Y-direction, and wafer W is disposed on a prescribed position by driving the XY table 4.
A probe card 5 provided with a plurality of probe pins 5A is arranged above the main chuck 3, and the probe card 5 is supported by an aligning mechanism 6. The aligning mechanism 6 is operated so as to permit the probe pins 5A to be positioned accurately above a plurality of electrode pads of the wafer W held by the main chuck 3. Also, a lift mechanism is arranged inside the main chuck 3. During the examining process, the wafer W is moved upward by the lift mechanism so as to allow the probe pins 5A to be brought into a mechanical and electrical contact with the electrode pads. Also, after the examining process, the wafer W is moved downward by the lift mechanism so as to cause the probe pins 5A to be separated mechanically and electrically from the electrode pads.
Also, a test head T of a tester is rotatably arranged on a head plate 7 defining the probe chamber 2, as shown in FIG. 1. The test head T is electrically connected to the probe card 5 via a performance board (not shown). The temperature of the wafer W disposed on the main chuck 3 is set at a prescribed temperature falling with a prescribed temperature range, e.g., a temperature range of between −40° C. and +150° C., and the temperature of the wafer W is maintained at the set temperature during the test. Also, during the test, a signal for the examination is transmitted from the tester to reach the probe pins 5A via the test head T and the performance board noted above, with the result that the signal for the examination is applied from the probe pins 5A to the electrode pads of the wafer W so as to examine the electrical characteristics of a plurality of semiconductor devices formed on the wafer W. Where the wafer W is set at a high-temperature not lower than the room temperature, the wafer W is heated to the prescribed temperature via a temperature control mechanism including the heating source provided in the main chuck 3 and, then, the electrical characteristics of the wafer are examined.
The circuit of the chip formed on the wafer W has been rendered ultra fine in recent years and the diameter of the wafer W itself has been much enlarged in recent years. In accordance with these tendencies, the diameter of the probe card 5 has been also enlarged in recent years. In accordance with the enlargement of the diameter, the probe card 5 is reinforced by a support frame 5B made of a metallic material such as stainless steel as shown in FIGS. 2A and 2B so as to impart a sufficiently rigid structure to the probe card 5. The probe card 5 is fixed to the head plate 7 by an annular holder 8 together with the support frame 5B. To be more specific, the probe card 5 is fastened and fixed to the holder 8 together with the support frame 5B by a plurality of fastening members 9A such as a screw. Also, the holder 8 is fastened and fixed to the head plate 7 via a plurality of fastening members 9B.
In the mechanism for fixing the probe card described above, a problem is generated in the case of examining the electrical characteristics of the wafer W in the initial stage of the heating under a high-temperature environment, e.g., a high-temperature environment of 100° C. To be more specific, the lower side of the probe card 5 or the holder 8 is more heated than the upper side by the heat radiated from the main chuck 3. As a result, the lower side is thermally expanded more greatly than the upper side, with the result that the probe card 5 or the holder 8 is bent. What should also be noted is that the probe card 5 is fixed to the inner circumferential edge portion of the holder 8. As a result, the probe card 5 is prevented from being elongated radially outward and is elongated radially inward so as to be bent downward, as shown in FIG. 2A. It should also be noted that the outer circumferential edge portion of the holder 8 is fixed to the head plate 7. As a result, the holder 8 is elongated radially inward so as to cause the probe card 5 to be further bent downward. Such being the situation, the probe pins 5A are displaced vertically downward so as to cause the probe pressures between the probe pins 5A and the electrode pads of the wafer W to be set greater than the preset values. As a result, the electrode pads and the underlayers thereof are bruised so as to invite a defective examination. Particularly, where the probe card 5 is reinforced by the support frame 5B as shown in FIGS. 2A and 2B, a serious problem is generated that the probe card 5 is much affected by the thermal expansion of the support frame 5B.
It should also be noted that, in the examination stage under a high-temperature, the probe card 5 and the support frame 5B are sufficiently heated so as to be thermally expanded, as shown in FIG. 2B. Also, since the holder 8 is sufficiently heated so as to be thermally expanded, an outward stress is exerted from the probe card 5 and the support frame 5B to the fastening member 9A. At the same time, an inward stress is exerted from the holder 8 to the fastening member 9A. Where such a function is generated, the probe card 5 is bent upward as shown in FIG. 2B, which is opposite to that shown in FIG. 2A. In this case, the probe pins 5A are moved upward so as to bring about possibly a defective contact. The phenomenon shown in FIGS. 2A and 2B is similarly generated in the case where the probe card 5 is reinforced by the support frame 5B.